1. Field of the Invention
The present invention relates generally to casting light alloy components, for example aluminum alloy components, and more particularly to casting components incorporating metal inserts.
One non-limiting example of such components is internal combustion engine cylinder blocks incorporating inserts consisting of cylinder liners.
2. Description of the Prior Art
To make some cast aluminum components, for example engine cylinder blocks, it is currently necessary to use at some locations inserts made from a material other than that from which the component is cast. In the case of light alloy engine blocks, the most widely used technology consists in integrally casting cast iron liners which, in the assembled engine, come into contact with the piston rings. The insert is given a satisfactory mechanical attachment surface, for example by machining helicoidal grooves into the external surface of the liners. If the liquid aluminum penetrates properly into them, the mechanical strength of the combination is satisfactory.
It appears that if the liners are placed in the mold cold, whether this is a metal mold (low-pressure or shell gravity type processes) or a green sand mold, for example as described in the document FR 2 775 917 A in the name of the applicant, it is not possible to guarantee correct coating of the cast iron liners by the liquid aluminum, whatever the conditions for preparing the surface of the machined insert (shot-blasting, degreasing, etc), and whatever the casting conditions (provided that they lie within a range of parameter values enabling an engine block free of functional defects to be obtained). This results in voids in the aluminum, caused by misruns and blowholes, at places on the outside surface of the liners, and in particular in the areas between the liners, which are functionally unacceptable because they seriously compromise the mechanical cohesion between the engine block and the liners.
One prior art method of overcoming this problem consists of heating the liners, either in a separate furnace, before they are inserted into the mold, in the case of processes using metal molds, or by boring orifices in the sand, in the case of processes using sand molds, through which electrical inductors are passed as far as the interior space of the liners, to heat the liners inductively in the mold before casting the metal.
However, in this type of application these heating techniques represent a penalty from the points of view of investment, complexity of use and control. Failing better solutions, these techniques are nevertheless used at present to make internal combustion engine blocks with integrally cast liners made of cast iron.
An object of the present invention is to alleviate these limitations of the prior art and to obtain good coating of the insert by the liquid aluminum alloy, combined with intimate contact between the insert and the aluminum alloy after solidification, without preheating the insert prior to casting the aluminum alloy.